<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="js/js01.js"></script>
    <script>
        // document.write('Hello!')
        alert('HelloWorld!')
        var i = "line line so easy, day day no bug!";
        alert(i + " =>> " + i);
        j = i.substr(5, 4)
        alert(i + " =>> " + j);
        k = i.substring(5, 15);
        alert(i + " =>> " + k);

    </script>
</head>
<body>

<script>
    document.write("<h1>666!</h1>")
</script>

</body>
</html>